The field of the invention relates to a control system for use with a bidirectional motor connected to vehicle accessories. More particularly, the system controls bidirectional electric d.c. motors that may be used with vehicle accessories such as power seats, power sunroofs, power mirrors, and power windows.
Modern automobiles include electric d.c. motors to control many vehicle accessories, thereby increasing the quality, convenience, and safety of automobile ownership and operation. Power accessories allow an automobile user to conveniently access automobile features and often provide a safety function to protect the automobile's occupants. An automobile user may conveniently activate many functions such as opening a window or adjusting a mirror with a simple push of a button.
For example, power seats are sometimes provided with a memory feature that permits a driver to have an electric motor automatically adjust the power seat to a previously set position. This feature enables several users, e.g. a husband and wife, to each store his or her own personal preferred seat adjustment position. Thereafter, the seat automatically adjusts to a position previously stored by that user when one of the drivers first enters the vehicle and activates the appropriate control.
This feature for automobile seats may require a memory capable of storing information corresponding to a first position of the seat, i.e. the current position, and a second position of the seat, i.e. the desired position. This memory may also include data for the seat backrest angle, the seat bottom linear position, tilt position, and so on.
One prior method to obtain this data was to attach sensors, such as potentiometers, to the seat components for producing electrical signals indicative of the seat component's position. Potentiometers have been a reliable way to obtain information about the position of the various seat components; however, this method includes the added expense of providing and installing potentiometers.
An alternative method to obtain seat position information is to count the number of commutation pulses generated by the electric motor that moves the seat. Assuming the motor has a predetermined number of poles and that each revolution of the motor causes the seat to move a known distance, the seat position may be related to the number of commutation pulses generated by the motor controlling the seat. Using commutation pulses to obtain information about the position of a vehicle seat eliminates the need and added cost for separate potentiometers. One way to use commutation pulses is related in U.S. Pat. No. 4,463,426 ("the '426 patent").
However, using the number of commutation pulses to determine the actual position of the seat has disadvantages. Since commutation pulses provide only a relative position of the seat to an arbitrary starting point, any inaccuracy in the pulse detection system may cause the seat position stored in memory to drift over time to a noticeably incorrect representation of the actual seat position. The vehicle user must then re-enter the desired position into memory after engaging a selector to manually control the motor that moves the seat to the desired position. For the foregoing reasons there is a need for a commutation pulse detection system for controlling automobile accessories such as power seats with improved position accuracy.
An object of this invention is to provide an improved control system that reduces errors associated with seat position memory operation. Another object of this invention is to provide a control system that can estimate when errors have occurred. Another object of the invention is to provide an improved control system that solves the problems and removes deficiencies present in the prior art.